NPS 22 Pipe Dimensions

Nominal size

NPS 22

Metric designator

DN 550

Outside diameter

22.000 in (558.8 mm)

Schedules listed

12

Standard weight wall

0.375 in (9.5 mm)

Extra strong wall

0.500 in (12.7 mm)

What NPS 22 is

NPS 22 pipe measures 22.000 in (558.8 mm) across the outside, so here the size designation and the outside diameter in inches are the same number. That holds from NPS 14 upward and for no size below it. The metric designator is DN 550, which is likewise a label and not a measurement in millimetres. Whatever the schedule, the outside diameter stays at 22.000 in (558.8 mm): a heavier wall grows inward and takes the difference out of the bore.

Less commonly stocked than the sizes either side of it; many piping size lists step from NPS 20 to NPS 24. B36.10M publishes no Schedule 40 wall for it.

Every schedule in NPS 22

Dimensions are given in inches, with the millimetre equivalent beneath in grey.

Inside diameter is OD − 2t. Weight is calculated for carbon steel as w = 10.69 × t × (OD − t) lb/ft and is the plain-end weight, excluding coatings, linings and fittings. Water-filled weight adds fresh water at 8.3454 lb per US gallon.

Reading the table

B36.10 lists 12 designations in NPS 22, which between them give 10 different wall thicknesses. The lightest is Schedule 5 at 0.188 in (4.8 mm) and the heaviest is Schedule 160 at 2.125 in (54.0 mm). Going from one to the other takes the bore from 21.624 in (549.2 mm) down to 17.750 in (450.8 mm), which cuts the flow area by 33% and raises the weight from 43.84 to 451.49 lb/ft, a factor of 10.3.

Standard weight equals Schedule 20 in this size. Extra strong equals Schedule 30. Where two designations share a wall they are the same pipe under two names, and either may appear on a mill certificate. The match is specific to the size, so it is the wall thickness in inches that should go on a requisition, not the designation alone.

For handling and support loads, a 20 ft length of standard weight NPS 22 pipe weighs about 1734 lb (786 kg) empty and 4809 lb (2181 kg) full of water. The water-filled figure is the one that governs pipe support spacing and the load during a hydrostatic test, including on lines that will carry gas or vapour in service.

Flow and pressure capacity by schedule

Two questions decide a schedule: how much the bore will carry, and how much pressure the wall will hold. The flow columns give the water flow through each bore at three velocities that bracket ordinary liquid service, from a pump suction line at the low end to a pump discharge line at the high end. The pressure columns are the ASME B31.3 pressure design equation solved for pressure, first on the nominal wall and then on the wall after the 12.5% mill under-tolerance that seamless pipe is allowed.

Flow is velocity × flow area. Pressure is P = 2·S·t / (D − 2·Y·t) with S = 20,000 psi, E = W = 1.0 and Y = 0.4: seamless carbon steel such as A106 Gr B at moderate temperature, with no corrosion allowance and no threading allowance. It is an illustration of the arithmetic, not a design rating.

The method behind both halves of that table is set out in the pipe sizing guide and the wall thickness guide, each with a worked example.

Flanges for NPS 22 pipe

ASME B16.5 publishes no flange in NPS 22 and ASME B16.9 no buttweld fitting. That is the practical meaning of an obsolete size: pipe of this diameter exists in old plant, but nothing standard is made to connect to it. New work uses the next size up or down.

Buttweld fittings for NPS 22 pipe

ASME B16.9 sets the dimensions of a buttweld fitting from the NPS alone, so the figures below hold for every schedule in the size. A long radius 90° elbow in NPS 22 measures 33.00 in (838.2 mm) from its centre to each end, which is the figure a piping layout adds for every change of direction. The fitting is still ordered to a schedule, because its wall has to match the pipe at the weld.

The cap is the exception to the rule above: its length is for walls up to a limiting thickness, and a heavier wall takes a longer cap. See the cap page.

Guides and comparisons for this page

NPS 22 in each schedule chart

Adjacent sizes